LHC searches for \({E}_T\)  plus jet signals place strong constraints on the interactions between quarks and DM mediated by a vector mediator [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}.
The corresponding cross sections can be calculated at next-to-leading order (NLO)
in MCFM [9]} and at NLO plus parton shower
in the POWHEG BOX [10]}. Some of the relevant diagrams are shown in Figure REF .
If the mediator is too heavy to be produced on-shell at the LHC and assuming equal vector couplings of the mediator to all quarks as well as \(g_\ell ^V = g_i^A = 0\) , the mono-jet cross section at the LHC is proportional to \((g_q^V)^2 \, (g_\chi ^V)^2\) . The same scaling applies if the mediator is forced to be off-shell because \(M_V < 2 m_\chi \)  so that decays into DM are kinematically forbidden.
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